Question

Why do so many cultures have divinities in similar roles?

Answer 1

The answer to your question is: Every culture has their own stories to tell and to help them cope up with uncontrollable circumstances in the environment. These stories maybe are myths and are powerful religious influences in the culture. Though there are differences between cultures somehow many cultures have divinities in similar roles through adaptations.

Answer 2

Cultures have similar divinities and deities due to their perception of  good and evil.  All cultures may have a different practice but all cultures know the concept of what is bad and what is good is very common in all culture. For example, in some cultures, their perception of natural disaster is associated with evil. They believe that these events occur because they have offended their god and thus the calamity was their punishment.